Cement slurries, cured cement and methods of making and use of these

ABSTRACT

Cement slurries, cured cements, and methods of making cured cement and methods of using cement slurries are provided. The cement slurries have, among other attributes, improved expanding capabilities and may be used, for instance, in the oil and gas drilling industry. The cement slurry comprises water, a cement precursor material, and an expanding agent. The expanding agent comprising at least a poly(lactic acid)-metal oxide nanocomposite. The metal oxide comprises MgO, CaO, or both, and the poly(lactic acid) comprises a carboxylic acid terminal group.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application Ser.No. 63/112,261 filed Nov. 11, 2020, the entire disclosure of which ishereby incorporated herein by reference.

TECHNICAL FIELD

Embodiments of the present disclosure generally relate to cementslurries and methods of making and using cement slurries and to curedcements and methods of making cured cement.

BACKGROUND

Cement slurries are used in the oil and gas industries, such as forcementing in oil and gas wells. Primary, remedial, squeeze, and plugcementing techniques can be used, for instance, to place cement sheathsin an annulus between casing and well formations, for well repairs, wellstability, or for well abandonment (sealing an old well to eliminatesafety hazards). These cement slurries must be able to consistentlyperform over a wide range of temperatures and conditions as cement setin an oil and gas well may be vulnerable to cyclic stresses imposed bypressure and temperature fluctuations. A brittle cement may crack andbreak under these stresses, reducing the integrity of the wellbore.

SUMMARY

Adding expanding agents to cement slurry can be vital to the strengthand expanding and performance properties of the cured cementcomposition. However, conventional expanding agents expand immediatelyupon contact with the water in the cement slurry, limiting the abilityof the cement slurry or cured cement to expand further once placeddownhole.

Accordingly, there is an ongoing need for cement slurries that areresistant to cyclic stresses and capable of expanding to seal againstwater seepage after downhole placement. Furthermore, cured cementshaving expanding characteristics prevent cracking and breaking undercyclic stresses. The present embodiments address these needs byproviding cement slurries and methods of making and using cementslurries that include an expanding agent that expands upon contact withwater in temperatures greater than 100° C., avoiding premature expansionat the mixing stage, at the surface of the well, or before curing. Theexpanding agent described herein include at least a poly(lacticacid)-metal oxide nanocomposite, a poly(acrylic acid)-metal oxidenanocomposite, or both, where the poly(lactic acid) or poly(acrylicacid) protects the metal oxide from premature contact with water beforedownhole placement. In particular, the poly(lactic acid) or poly(acrylicacid) degrades when in contact with water in temperatures greater than100° C., thereby allowing the water to contact the metal oxide and formexpanding crystals to seal against water seepage. Specifically, thepoly(lactic acid) or poly(acrylic acid) may degrade by undergoingdepolymerization when in contact with water in temperatures greater than100° C., which means that the long polymer chains undergo scission toform short chains that further break down to form monomers. In the caseof polyacrylic acid, degradation at high temperature leads to theformation of anhydrides and aromatic chars. The degradation products ofpoly(acrylic acid) do not lead to the formation of acrylic acid monomeror do not provide a pathway for regeneration of poly(acrylic acid).

In one embodiment, a cement slurry is provided that comprises water, acement precursor material, and an expanding agent. The expanding agentcomprising at least a poly(lactic acid)-metal oxide nanocomposite. Themetal oxide comprises MgO, CaO, or both, and the poly(lactic acid)comprises a carboxylic acid terminal group.

In another embodiment, a method of cementing a casing in a wellbore isprovided. The method comprises pumping a cement slurry into an annulusbetween the casing and the wellbore. The cement slurry comprises water,a cement precursor material, and an expanding agent. The expanding agentcomprises at least a poly(lactic acid)-metal oxide nanocomposite. Themetal oxide comprises MgO, CaO, or both, and the poly(lactic acid)comprises a carboxylic acid terminal group. The method further comprisescuring the cement slurry to cement the casing in the wellbore.

In a further embodiment, a method of producing a poly(lactic acid)-metaloxide nanocomposite is provided. The method comprises reactingpoly(lactic acid) with MgO nanocomposites, CaO nanocomposites, or both.The method further comprises reacting the poly(lactic acid) with ananhydride to add a carboxylic acid terminal group to the poly(lacticacid), thereby forming the poly(lactic acid)-metal oxide nanocomposite.

Additional features and advantages of the described embodiments will beset forth in the detailed description which follows, and in part will bereadily apparent to those skilled in the art from that description orrecognized by practicing the described embodiments, including thedetailed description which follows as well as the claims.

DETAILED DESCRIPTION

As used throughout this disclosure, the term “cement slurry” refers to acomposition comprising a cement precursor that is mixed with at leastwater to form cement. The cement slurry may contain calcined alumina(Al₂O₃), silica (SiO₂), calcium oxide (CaO, also known as lime), ironoxide (FeO), magnesium oxide (MgO), clay, sand, gravel, and mixtures ofthese.

As used throughout this disclosure, “curing” refers to providingadequate moisture, temperature and time to allow the concrete to achievethe desired properties (such as hardness) for its intended use throughone or more reactions between the water and the cement precursormaterial.

As used throughout this disclosure, “drying” refers to merely allowingthe cement to achieve a moisture condition appropriate for its intendeduse, which may only involve physical state changes as opposed tochemical reactions.

As used throughout this disclosure, the term “retarder” refers to achemical agent used to increase the thickening time of cement slurriesto enable proper placement of the cement slurry within the wellbore. Theneed for cement retardation increases with depth due to the greater timerequired to complete the cementing operation and the effect of increasedtemperature on the cement-setting process.

As used throughout this disclosure, the term “subsurface formation”refers to a body of rock that is sufficiently distinctive and continuousfrom the surrounding rock bodies that the body of rock can be mapped asa distinct entity. A subsurface formation is, therefore, sufficientlyhomogenous to form a single identifiable unit containing similarrheological properties throughout the subsurface formation, including,but not limited to, porosity and permeability. A subsurface formation isthe fundamental unit of lithostratigraphy.

As used throughout this disclosure, the term “thickening time” refers toa measurement of the time during which a cement slurry remains in afluid state and is capable of being pumped. Thickening time is assessedunder downhole conditions using a pressurized consistometer that plotsthe viscosity of a slurry over time under the anticipated temperatureand pressure conditions. The end of the thickening time isconventionally about 50 or 70 Bearden units of consistency (Be), adimensionless quantity with no direction conversion factor to morecommon units of viscosity. The Bearden units of consistency is measuredon a scale from 1 to 100 where difficult pumping begins at 50 Be andcement is completely set at 100 Be.

As used throughout this disclosure, the term “wellbore” refers to thedrilled hole or borehole, including the openhole or uncased portion ofthe well. Borehole may refer to the void space defined by the wellborewall, where the rock face that bounds the drilled hole defines theborehole.

Embodiments of the present disclosure relate to cement slurries andcured cements with elasticity and self-healing capabilities. Embodimentsof the present disclosure also relate to methods of producing and usingcement slurries, in some particular embodiments, for use in the oil andgas industries.

Oil and gas wells may be formed in subsurface formations. The wellboremay serve to connect natural resources, such as petrochemical products,to a ground level surface. In some embodiments, a wellbore may be formedin the subsurface formation, which may be formed by a drillingprocedure.

In some instances, a casing may be inserted into the wellbore. Thecasing may be a pipe which has a diameter less than that of thewellbore. Generally, the casing may be lowered into the wellbore suchthat the bottom of the casing reaches to a region near the bottom of thewellbore. In some embodiments, the casing may be cemented by inserting acement slurry into the annulus region between the outer edge of thecasing and the edge of the wellbore (the surface of the subsurfaceformation). The cement slurry may be inserted into the annular region bypumping the cement slurry into the interior portion of the casing, tothe bottom of the casing, around the bottom of the casing, into theannular region, or a combination of some or all of these. The cementslurry may displace the drilling fluid, pushing it to the top of thewell. In some embodiments, a spacer fluid may be used as a bufferbetween the cement slurry and the drilling fluid. The spacer fluiddisplaces and removes the drilling fluid before the cement slurry ispumped into the well to prevent contact between the drilling fluid andthe cement slurry. Following the insertion of an appropriate amount ofcement slurry into the interior region of the casing, in someembodiments, a displacement fluid may be utilized to push the cementslurry out of the interior region of the casing and into the annularregion. This displacement may cause the entirety of the spacer fluid anddrilling fluid to be removed from the annular region, out the top of thewellbore. The cement slurry may then be cured or otherwise allowed toharden.

To ensure the stability and safety of a well, it is important that thecured cement maintains integrity and isolates the wellbore from thesurrounding subsurface formations. If the cement cracks or degradesunder cyclic stresses, wellbore integrity and isolation may be lost,resulting in undesirable fluid communication between the wellbore andsurrounding subsurface formations. Not intending to be limited bytheory, this fluid communication may result in drilling fluid loss fromthe wellbore into the surrounding subsurface formation or in decreasedwellbore pressure, possibly leading to a well control event. Therefore,wellbore integrity and isolation are critical to effective productionand use of a wellbore.

The present disclosure provides cement slurries and cured cements thatmay have, among other attributes, expanding capabilities to addressthese concerns. The cement slurry of the present disclosure includeswater, a cement precursor material, and an expanding agent.

The cement precursor material may be any suitable material which, whenmixed with water, can be cured into a cement. The cement precursormaterial may be a hydraulic or a non-hydraulic cement precursor. Ahydraulic cement precursor material refers to a mixture of limestone,clay and gypsum burned together under extreme temperatures that maybegin to harden instantly or within a few minutes while in contact withwater. A non-hydraulic cement precursor material refers to a mixture oflime, gypsum, plasters and oxychloride. A non-hydraulic cement precursormay take longer to harden or may require drying conditions for properstrengthening, but often is more economically feasible. A hydraulic ornon-hydraulic cement precursor material may be chosen based on thedesired application of the cement slurry of the present disclosure. Insome embodiments, the cement precursor material may be Portland cementprecursor, for example, Class G Portland Cement. Portland cementprecursor is a hydraulic cement precursor (cement precursor materialthat not only hardens by reacting with water but also forms awater-resistant product) produced by pulverizing clinkers, which containhydraulic calcium silicates and one or more of the forms of calciumsulfate as an inter-ground addition.

The cement precursor material may include calcium hydroxide, silicates,oxides, belite (Ca₂SiO₅), alite (Ca₃SiO₄), tricalcium aluminate(Ca₃Al₂O₆), tetracalcium aluminoferrite (Ca₄Al₂Fe₂O₁₀), brownmillerite(4CaO·Al₂O₃·Fe₂O₃), gypsum (CaSO₄·2H₂O), sodium oxide, potassium oxide,limestone, lime (calcium oxide), hexavalent chromium, trivalentchromium, calcium aluminate, silica sand, silica flour, hematite,manganese tetroxide, or combinations of these. The cement precursormaterial may include Portland cement, siliceous fly ash, calcareous flyash, slag cement, silica fume, quartz, or combinations of any of these.Silica flour is a finely ground crystalline silica with a molecularformula of SiO₂ and with a grain size ranging from 1 to 500 microns(μm), from 10 to 500 microns, from 10 to 100 microns, from 10 to 80microns, from 10 to 50 microns, from 10 to 20 microns, from 20 to 100microns, from 20 to 80 microns, from 20 to 50 microns, from 50 to 100microns, from 50 to 80 microns, or from 80 to 100 microns.

Water may be added to the cement precursor material to produce theslurry. The water may be distilled water, deionized water, or tap water.In some embodiments, the water may contain additives or contaminants.For instance, the water may include freshwater or seawater, natural orsynthetic brine, or salt water. In some embodiments, salt or otherorganic compounds may be incorporated into the water to control certainproperties of the water, and thus the cement slurry, such as density.Without being bound by any particular theory, increasing the saturationof water by increasing the salt concentration or the level of otherorganic compounds in the water may increase the density of the water,and thus, the cement slurry. Suitable salts may include, but are notlimited to, alkali metal chlorides, hydroxides, or carboxylates. In someembodiments, suitable salts may include sodium, calcium, cesium, zinc,aluminum, magnesium, potassium, strontium, silicon, lithium, chlorides,bromides, carbonates, iodides, chlorates, bromates, formates, nitrates,sulfates, phosphates, oxides, fluorides, vanadium, zirconium, orcombinations of these.

In some embodiments, the cement slurry may contain from 10 weightpercent (wt. %) to 70 wt. % by weight of cement precursor (BWOC) water.In some embodiments, the cement slurry may contain from 10 wt. % to 40wt. %, from 10 wt. % to 30 wt. %, from 10 wt. % to 20 wt. %, from 20 wt.% to 40 wt. %, from 25 wt. % to 35 wt. %, or from 20 wt. % to 30 wt. %BWOC water. The cement slurry may contain 30 wt. % BWOC water.

As previously stated, along with the cement precursor material andwater, the cement slurry further includes an expanding agent. Inembodiments, the expanding agent may include at least a poly(lacticacid)-metal oxide nanocomposite. Alternatively or additionally, theexpanding agent may include at least a poly(acrylic acid)-metal oxidenanocomposite. In embodiments, the metal oxide of the poly(lacticacid)-metal oxide nanocomposite or the poly(acrylic acid)-metal oxidenanocomposite comprises MgO, CaO, or both.

The poly(lactic acid) may include a carboxylic acid terminal group. Inembodiments, the poly(lactic acid) having the carboxylic acid terminalgroup may be a reaction product of poly(lactic) acid and succinicanhydride, maleic anhydride, or both.

The poly(acrylic acid) may include a t-butyl terminal group, anisobornyl terminal group, or both.

In embodiments where the expanding agent includes at least a poly(lacticacid)-metal oxide nanocomposite, the poly(lactic acid)-metal oxidenanocomposite may have a structure of:

where XO is the metal oxide, such as alkaline earth metal oxides, and xis from 1 to 100, from 1 to 75, from 1 to 50, from 1 to 25, from 25 to100, from 25 to 75, from 25 to 50, from 50 to 100, from 50 to 75, orfrom 75 to 100. Alkaline earth metal oxides may include BeO, MgO, CaO,SrO, BaO, RaO, or combinations thereof.

In embodiments where the expanding agent includes at least apoly(acrylic acid)-metal oxide nanocomposite where the poly(acrylicacid) has a t-butyl terminal group, the poly(acrylic acid)-metal oxidenanocomposite may have a structure of:

where XO is the metal oxide; a ranges from 1 to 100, from 1 to 75, from1 to 50, from 1 to 25, from 25 to 100, from 25 to 75, from 25 to 50,from 50 to 100, from 50 to 75, or from 75 to 100; and b ranges from 1 to100, from 1 to 75, from 1 to 50, from 1 to 25, from 25 to 100, from 25to 75, from 25 to 50, from 50 to 100, from 50 to 75, or from 75 to 100.

In embodiments where the expanding agent includes at least apoly(acrylic acid)-metal oxide nanocomposite where the poly(acrylicacid) has an isobornyl terminal group, the poly(acrylic acid)-metaloxide nanocomposite may have a structure of:

where XO is the metal oxide; a ranges from 1 to 100, from 1 to 75, from1 to 50, from 1 to 25, from 25 to 100, from 25 to 75, from 25 to 50,from 50 to 100, from 50 to 75, or from 75 to 100; and b ranges from 1 to100, from 1 to 75, from 1 to 50, from 1 to 25, from 25 to 100, from 25to 75, from 25 to 50, from 50 to 100, from 50 to 75, or from 75 to 100.

The cement slurry may include from 5 to 25 wt. %, from 5 to 20 wt. %,from 5 to 17 wt. %, from 5 to 15 wt. %, from 5 to 12 wt. %, from 5 to 10wt. %, from 5 to 7 wt. %, from 7 to 25 wt. %, from 7 to 20 wt. %, from 7to 17 wt. %, from 7 to 15 wt. %, from 7 to 12 wt. %, from 7 to 10 wt. %,from 10 to 25 wt. %, from 10 to 20 wt. %, from 10 to 17 wt. %, from 10to 15 wt. %, from 10 to 12 wt. %, from 12 to 25 wt. %, from 12 to 20 wt.%, from 12 to 17 wt. %, from 12 to 15 wt. %, from 15 to 25 wt. %, from15 to 20 wt. %, from 15 to 17 wt. %, from 17 to 25 wt. %, from 17 to 20wt. %, or from 20 to 25 wt. % by weight of cement precursor material(BWOC) expanding agent.

In embodiments in which the expanding agent comprises at least apoly(acrylic acid)-metal oxide nanocomposite, the cement slurry mayfurther comprise from 15 to 100 mol. %, from 15 to 90 mol. %, from 15 to80 mol. %, from 15 to 75 mol. %, from 15 to 70 mol. %, from 15 to 60mol. %, from 15 to 50 mol. %, from 15 to 40 mol. %, from 15 to 30 mol.%, from 15 to 25 mol. %, from 15 to 20 mol. %, from 20 to 100 mol. %,from 20 to 90 mol. %, from 20 to 80 mol. %, from 20 to 75 mol. %, from20 to 70 mol. %, from 20 to 60 mol. %, from 20 to 50 mol. %, from 20 to40 mol. %, from 20 to 30 mol. %, from 20 to 25 mol. %, from 25 to 100mol. %, from 25 to 90 mol. %, from 25 to 80 mol. %, from 25 to 75 mol.%, from 25 to 70 mol. %, from 25 to 60 mol. %, from 25 to 50 mol. %,from 25 to 40 mol. %, from 25 to 30 mol. %, from 30 to 100 mol. %, from30 to 90 mol. %, from 30 to 80 mol. %, from 30 to 75 mol. %, from 30 to70 mol. %, from 30 to 60 mol. %, from 30 to 50 mol. %, from 30 to 40mol. %, from 40 to 100 mol. %, from 40 to 90 mol. %, from 40 to 80 mol.%, from 40 to 75 mol. %, from 40 to 70 mol. %, from 40 to 60 mol. %,from 40 to 50 mol. %, from 50 to 100 mol. %, from 50 to 90 mol. %, from50 to 80 mol. %, from 50 to 75 mol. %, from 50 to 70 mol. %, from 50 to60 mol. %, from 60 to 100 mol. %, from 60 to 90 mol. %, from 60 to 80mol. %, from 60 to 75 mol. %, from 60 to 70 mol. %, from 70 to 100 mol.%, from 70 to 90 mol. %, from 70 to 80 mol. %, from 70 to 75 mol. %,from 75 to 90 mol. %, from 75 to 80 mol. %, or from 80 to 90 mol. % acidcatalyst relative to the number of moles of tert-butyl and isobornylgroups in the block copolymer. The acid catalyst may include sulfonicacid, hydrochloric acid, trifluoroacetic acid, aqueous phosphoric acid,molecular iodine, an acidic metal catalyst such as zinc bromide, orcombinations thereof. In embodiments, the sulfonic acid may includepara-toluenesulfonic acid.

The cement slurry may have a density of from 10 to 20 pounds per gallon(ppg), from 10 to 18 ppg, from 10 to 16 ppg, from 10 to 15 ppg, from 10to 14 ppg, from 10 to 12 ppg, from 12 to 20 ppg, from 12 to 18 ppg, from12 to 16 ppg, from 12 to 15 ppg, from 12 to 14 ppg, from 14 to 20 ppg,from 14 to 18 ppg, from 14 to 16 ppg, from 14 to 15 ppg, from 15 to 20ppg, from 15 to 18 ppg, from 15 to 16 ppg, from 16 to 20 ppg, from 16 to18 ppg, or from 18 to 20 ppg.

In some embodiments, the cement slurry may contain at least one additiveother than the expanding agent. The one or more additives may be anyadditives known to be suitable for cement slurries. As non-limitingexamples, suitable additives may include accelerators, retarders,extenders, suspending agents, weighting agents, fluid loss controlagents, lost circulation control agents, surfactants, antifoamingagents, and combinations of these. The suspending agents may include atleast one of a copolymer of N,N-dimethylacrylamide and sodium2-acrylamido-2-methyl propane sulfonate, and hydroxyethyl cellulose.

In some embodiments, the cement slurry may contain from 0.1 to 10% BWOCof the one or more additives based on the total weight of the cementslurry. For instance, the cement slurry may contain from 0.1 to 8% BWOCof the one or more additives, from 0.1 to 5% BWOC of the one or moreadditives, or from 0.1 to 3% BWOC of the one or more additives. Thecement slurry may contain from 1 to 10% BWOC of the one or moreadditives, from 1 to 8% BWOC, from 1 to 5% BWOC, or from 1 to 3% BWOC ofthe one or more additives. In some embodiments, the cement slurry maycontain from 3 to 5% BWOC, from 3 to 8% BWOC, from 3 to 10% BWOC, orfrom 5 to 10% BWOC of the one or more additives.

In some embodiments, the one or more additives may include a dispersantcontaining one or more anionic groups. For instance, the dispersant mayinclude synthetic sulfonated polymers, lignosulfonates with carboxylategroups, organic acids, hydroxylated sugars, or combinations of any ofthese. Without being bound by any particular theory, in someembodiments, the anionic groups on the dispersant may be adsorbed on thesurface of the cement particles to impart a negative charge to thecement slurry. The electrostatic repulsion of the negatively chargedcement particles may allow the cement slurry to be dispersed and morefluid-like, improving flowability. This may allow for one or more ofturbulence at lesser pump rates, reduction of friction pressure whenpumping, reduction of water content, and improvement of the performanceof fluid loss additives.

In some embodiments, the one or more additives may alternatively oradditionally include a fluid loss additive. In some embodiments, thecement fluid loss additive may include non-ionic cellulose derivatives.In some embodiments, the cement fluid loss additive may behydroxyethylcellulose (HEC). In other embodiments, the fluid lossadditive may be a non-ionic synthetic polymer (for example, polyvinylalcohol or polyethyleneimine). In some embodiments, the fluid lossadditive may include bentonite, which may additionally viscosify thecement slurry and may, in some embodiments, cause additional retardationeffects.

In some embodiments, the cement slurry may contain from 0.1% BWOC to 10%BWOC of one or more fluid loss additives, the one or more dispersants,or both. The cement slurry may contain from 0.02 to 90 pounds per barrel(lb/bbl) of the fluid loss additives, the one or more dispersants, orboth based on the total weight of the cement slurry. For instance, thecement slurry may contain from 0.1 to 90 lb/bbl, from 0.1 to 75 lb/bbl,from 0.1 to 50 lb/bbl, from 1 to 90 lb/bbl, from 1 to 50 lb/bbl, from 5to 90 lb/bbl, or from 5 to 50 lb/bbl of the fluid loss additives, theone or more dispersants, or both.

Embodiments of the disclosure also relate to methods of producing thepoly(lactic acid)-metal oxide nanocomposites previously described. Themethod for producing the poly(lactic acid)-metal oxide nanocompositesmay include reacting poly(lactic acid) with MgO nanocomposites, CaOnanocomposites, or both. The method may further include reacting thepoly(lactic acid) with an anhydride to add a carboxylic acid terminalgroup to the poly(lactic acid), thereby forming the poly(lacticacid)-metal oxide nanocomposites. The anhydride may be any of theanhydrides as previously described. Similarly, the poly(lacticacid)-metal oxide nanocomposite may have any of the structures aspreviously described. The reaction mechanism including reactingpoly(lactic acid) with an MgO nanoparticle, and further reacting MgOnanocomposite with the succinic anhydride to form the poly(lactic acid)with a carboxylic acid terminal group is shown below as a non-limitingexample and solely for illustrative purposes.

It is to be understood that any of the components may be substitutedwith any other component previously described.

Embodiments of the disclosure also relate to methods of producing thepoly(acrylic acid)-metal oxide nanocomposites previously described. Themethod for producing the poly(acrylic acid) metal oxide nanocompositesmay include synthesizing poly(acrylic acid) comprising a t-butylterminal group, an isobornyl terminal group, or both via reversibleaddition-fragmentation chain transfer (RAFT) polymerization.

RAFT polymerization require the use of (I) initiators, (II) RAFT agents,and (III) monomers. In embodiments, the monomers may include tert-butylacrylate, isobornyl acrylate, or both.

The initiators begin the polymerization reactions. The initiator mayinclude 4,4′-azobis(4-cyanovaleric acid), any of the followingcomponents, or combinations thereof. In embodiments, the initiator mayinclude hydrogen peroxides, azo compounds, redox systems, alkali metals,ammonium persulfates, ammonium perborates, ammonium perchlorates, alkalimetal persulfates, or combinations thereof. The redox systems mayinclude hydrogen peroxide, alkyl peroxide, alkyl peresters, alkylpercarbonates, iron salt, titanous salt, zinc formaldehyde sulfoxylateor sodium formaldehyde sulfoxylate, or combinations thereof. Inembodiments, the alkali metals, ammonium persulfates, ammoniumperborates, or ammonium perchlorates may be used in combination with analkali metal bisulfite, reducing sugars, or both. The alkali metalbisulfite may include sodium metabisulfite. In embodiments, the alkalimetal persulfates may be used in combinations with an arylphosphinicacid, reducing sugars, or both. The arylphosphinic acid may includebenzenephosphonic acid.

The hydrogen peroxides may include tert-butyl hydroperoxide, cumenehydroperoxide, t-butyl peroxyacetate, t-butyl peroxybenzoate, t-butylperoxyoctoate, t-butyl peroxyneodecanoate, t-butyl peroxyisobutyrate,lauroyl peroxide, t-amyl peroxypivalate, t-butyl peroxypivalate, dicumylperoxide, benzoyl peroxide, potassium persulfate, ammonium persulfate,or combinations thereof.

An azo compound is a compound bearing the functional group diazenylR—N═N—R′, in which R and R′ can be either aryl or alkyl. The azocompounds may include 4,4′-Azobis(4-cyanovaleic acid),2,2′-Azobis(2-methylpropionitrile), 2,2′-azobis(isobutyronitrile),2,2′-azobis(2-butanenitrile), 4,4′-azobis(4-pentanoic acid),1,1′-azobis(cyclohexanecarbonitrile), 2-(t-butylazo)-2-cyanopropane,2,2′-azobis[2-methyl-N-(1,1)-bis(hydroxymethyl)-2-hydroxyethyl]-propionamide,2,2′-azobis(2-methyl-N-hydroxyethyl]propionamide,2,2′-azobis(N,N′-dimethyleneisobutyramidine) dichloride,2,2′-azobis(2-amidinopropane) dichloride,2,2′-azobis(N,N′-dimethyleneisobutyramide),2,2′-azobis(2-methyl-N-[1,1-bis(hydroxy-methyl)-2-hydroxyethyl]propionamide),2,2′-azobis(2-methyl-N-[1,1-bis(hydroxy-methyl)ethyl]propionamide),2,2′-azobis[2-methyl-N-(2-hydroxyethyl)propionamide],2,2′-azobis(isobutyramide) dehydrate, or combinations thereof. Inembodiments, the initiator may include 4,4′-azobis(4-cyanovaleic acid),2,2′-azobis(2-methylpropionitrile), or both. The chemical structure of4,4′-azobis(4-cyanovaleic acid) and 2,2′-azobis(2-methylpropionitrile)are shown below:

The initiators may have an initiation temperature of from 50° C. to 80°C., from 50° C. to 75° C., from 50° C. to 70° C., from 50° C. to 65° C.,from 50° C. to 60° C., from 50° C. to 55° C., from 55° C. to 80° C.,from 55° C. to 75° C., from 55° C. to 70° C., from 55° C. to 65° C.,from 55° C. to 60° C., from 60° C. to 80° C., from 60° C. to 75° C.,from 60° C. to 70° C., from 60° C. to 65° C., from 65° C. to 80° C.,from 65° C. to 75° C., from 65° C. to 70° C., from 70° C. to 80° C.,from 70° C. to 75° C., or from 75° C. to 80° C. Without intending to bebound by theory, it may be desirable to have the initiation temperaturebe less than 100° C., less than 90° C., less than 85° C., less than 80°C., less than 75° C., less than 70° C., or less than 65° C. in order tobe lower than a boiling temperature of the solvent.

The general structure of a RAFT agent is:

where Z referents a hydrogen atom, a chlorine atom, a sulfur atom, anoptionally substituted alkyl or optionally substituted aryl radical, anoptionally substituted heterocycle, an optionally substituted alkylthioradical, an optionally substituted arylthio radical, an optionallysubstituted alkylselenium radical, an optionally substitutedarylselenium radical, an optionally substituted alkoxy radical, anoptionally substituted aryloxy radical, an optionally substituted aminoradical, an optionally substituted hydrazine radical, an optionallysubstituted alkoxycarbonyl radical, an optionally substitutedaryloxycarbonyl radical, an optionally substituted acycloxy or carboxylradical, an optionally substituted aroyloxy radical, an optionallysubstituted carbamoyl radical, a cyano radical, a dialkyl- ordiarylphosphonato radical, a dialkyl-phosphinato or diaryl-phosphinatoradical, or a polymer chain; and R′ represents an optionally substitutedalkyl, acyl, aryl, aralkyl, alkenyl or alkynyl group; a saturated orunsaturated, aromatic, optionally substituted carbocycle or heterocycle;or a polymer chain, where the polymer chain may be hydrophilic.

The R′ or Z groups, when they are substituted, can be substituted byoptionally substituted phenyl groups, optionally substituted aromaticgroups, saturated or unsaturated carbocycles, saturated or unsaturatedheterocycles, or groups selected from the following: alkoxycarbonyl oraryloxycarbonyl (—COOR), carboxyl (—COOH), acyloxy (—O₂CR), carbamoyl(—CONR₂), cyano (—CN), alkylcarbonyl, alkylarylcarbonyl, arylcarbonyl,arylalkylcarbonyl, phthalimido, maleimido, succinimido, amidino,guanidimo, hydroxyl (—OH), amino (—NR₂), halogen, perfluoroalkylC_(n)F_(2n+1), allyl, epoxy, alkoxy (—OR), S-alkyl, S-aryl, Se-alkyl,Se-aryl groups exhibiting a hydrophilic or ionic nature, such as alkalimetal salts of carboxylic acids, alkali metal salts of sulfonic acids,polyalkylene oxide (PEO, PPO) chains, cationic substituents (quaternaryammonium salts), R representing an alkyl or aryl group, or a polymerchain.

The RAFT agents may include sulfur, nitrogen, oxygen, selenium,phosphorus, or combinations thereof. In embodiments, the RAFT agent mayinclude sulfur and one or more of the group consisting of nitrogen,oxygen, selenium, and phosphorus. In embodiments, the RAFT agent mayinclude 2-(Butylthiocarbonothioylthio)propanoic acid. Without intendingto be bound by theory, the RAFT agents include sulfur to ensure chemicalstability at temperatures greater than or equal to 100° C. and less thanor equal to 140° C., greater than or equal to 100° C. and less than orequal to 130° C., greater than or equal to 100° C. and less than orequal to 120° C., greater than or equal to 110° C. and less than orequal to 140° C., greater than or equal to 110° C. and less than orequal to 130° C., greater than or equal to 110° C. and less than orequal to 120° C., greater than or equal to 120° C. and less than orequal to 140° C., or greater than or equal to 120° C. and less than orequal to 130° C.

In embodiments, the structure of the RAFT agent may be:

where c is from 1 to 20, from 1 to 15, from 1 to 10, from 1 to 5, from 1to 4, from 1 to 3, from 1 to 2, from 2 to 20, from 2 to 15, from 2 to10, from 2 to 5, from 2 to 4, from 2 to 3, from 3 to 20, from 3 to 15,from 3 to 10, from 3 to 5, from 3 to 4, from 4 to 20, from 4 to 15, from4 to 10, from 4 to 5, from 5 to 20, from 5 to 15, from 5 to 10, from 10to 20, from 10 to 15, or from 15 to 20. In embodiments, c may be 1, 2,3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20.

RAFT polymerization may occur as illustrated below:

In embodiments, the RAFT polymerization may include 2 steps. The firststep may be the initiation of the polymerization reaction, as shownbelow:

The second step may be the chain transfer reaction between radicals andthe RAFT agent as shown below:

The method for producing the poly(acrylic acid) metal oxidenanocomposites may further include grafting the poly(acrylic acid) ontoa XO metal oxide nanocomposites, CaO nanocomposites, or both, therebyforming the poly(acrylic acid)-metal oxide nanocomposite. The reactionmechanism including reacting poly(acrylic acid) having an t-butylterminal group with a XO metal oxide nanoparticle is shown below as anon-limiting example and solely for illustrative purposes.

It is to be understood that any of the components may be substitutedwith any other component previously described.

The reaction mechanism including reacting poly(acrylic acid) having anisobornyl terminal group with a XO metal oxide nanoparticle is shownbelow as a non-limiting example and solely for illustrative purposes.

It is to be understood that any of the components may be substitutedwith any other component previously described.

Embodiments of the disclosure also relate to methods of producing thecement slurries previously described. In some embodiments, the methodfor producing a cement slurry may include mixing water with a cementprecursor material and the expanding agent to produce a cement slurry.The water, cement precursor material, and expanding agent may be inaccordance with any of the embodiments previously described. The cementslurry may include one or more additives, including but not limited todefoamers, dispersants, and fluid loss additives. The mixing step, insome embodiments, may involve shearing the water, cement precursormaterial, expanding agent, and, optionally, other additives at asuitable speed for a suitable period of time to form the cement slurry.In one embodiment, the mixing may be done in the lab using a standardAPI blender for 15 seconds at 4,000 rotations per minute (RPM) and 35seconds at 12,000 RPM. The equation of mixing energy is:

$\begin{matrix}{\frac{E}{M} = \frac{k\;\omega^{2}t}{V}} & {{EQUATION}\mspace{14mu} 1}\end{matrix}$whereE=Mixing energy (kiloJoules)M=Mass of slurry (kilograms)k=6.1×10⁻⁸ meters to the fifth power per second (constant foundexperimentally)ω=Rotational speed (radians/s)t=Mixing time (seconds)V=Slurry volume (cubic meters)

Further embodiments of the present disclosure relate to methods of usingthe cement slurries previously described. In some embodiments, themethod may include pumping the cement slurry into a location to becemented and curing the cement slurry by allowing the water and thecement precursor material to react. The location to be cemented may, forinstance, be a well, a wellbore, or an annulus.

Cementing is performed when the cement slurry is deployed into the wellvia pumps, displacing the drilling fluids still located within the welland replacing them with cement. The cement slurry flows to the bottom ofthe wellbore through the casing, which will eventually be the conduitthrough which the hydrocarbons flow to the surface. From there, thecement slurry fills in the space between the casing and the wellborewall, and hardens. This creates a seal so that outside materials cannotenter the well flow as well as permanently positions the casing inplace. In preparing a well for cementing it is important to establishthe amount of cement required for the job. This may be done by measuringthe diameter of the borehole along its depth using a caliper log.Utilizing both mechanical and sonic means, multi-finger caliper logsmeasure the diameter of the well at numerous locations simultaneously inorder to accommodate for irregularities in the wellbore diameter anddetermine the volume of the open hole.

In some embodiments, curing the cement slurry may refer to passivelyallowing time to pass under suitable conditions upon which the cementslurry may harden or cure through allowing one or more reactions betweenthe water and the cement precursor material. Suitable conditions may beany time, temperature, pressure, or humidity known in the cementindustry to cure a cement composition. In some embodiments, suitablecuring conditions may be ambient conditions. Curing may also involveactively hardening or curing the cement slurry by, for instance,introducing a curing agent to the cement slurry, providing heat or airto the cement slurry, manipulating the environmental conditions of thecement slurry to facilitate reactions between the water and the cementprecursor, or a combination of these. Usually, the cement will be curedand convert from slurry to solid due to subsurface formation conditions,temperature, and pressure.

In some embodiments, curing may occur at a relative humidity of greaterthan or equal to 80% in the cement slurry and a temperature of greaterthan or equal to 50° F. for a time period of from 1 to 14 days. Curingmay occur at a relative humidity of from 80% to 100%, such as from 85%to 100%, or 90% to 100%, or from 95% to 100% relative humidity in thecement slurry. The cement slurry may be cured at temperatures of greaterthan or equal to 50° F., such as greater than or equal to 75° F.,greater than or equal to 80° F., greater than or equal to 100° F.,greater than or equal to 120° F., or greater than or equal to 180° F.The cement slurry may be cured at temperatures of from 50° F. to 250°F., or from 50° F. to 200° F., or from 50° F. to 150° F., or from 50° F.to 120° F., or from 50° F. to 180° F. In some instances, the temperaturemay be as great as 200° F., 300° F., 400° F., or 500° F. The cementslurry may be cured at pressures of greater than or equal to 20 poundsper square inch (psi), greater than or equal to 200 psi, greater than orequal to 500 psi, greater than or equal to 1000 psi, greater than orequal to 2000 psi, or greater than or equal to 3000 psi. The cementslurry may be cured at pressures of from 20 psi to 5000 psi, or from 200psi to 5000 psi, or from 200 psi to 3000 psi, or from 500 psi to 2000psi, or from 500 psi to 3000 psi. In some instances, the pressure may beas great as 1000 psi, 2000 psi, 3000 psi, 5000 psi, or 10000 psi. Thecement slurry may be cured for from 1 day to 14 days, such as from 3 to14 days, or from 5 to 14 days, or from 7 to 14 days, or from 1 to 4days, or from 4 to 7 days.

Further embodiments of the present disclosure relate to particularmethods of cementing a casing in a wellbore. The method may includepumping a cement slurry into an annulus between a casing and a wellboreand curing the cement slurry. The cement slurry may be in accordancewith any of the embodiments previously described. Likewise, curing thecement slurry may be in accordance with any of the embodimentspreviously described. As stated previously, cementing is performed whenthe cement slurry is deployed into the well via pumps, displacing thedrilling fluids still located within the well and replacing them withcement. The cement slurry flows to the bottom of the wellbore throughthe casing, which will eventually be the pipe through which thehydrocarbons flow to the surface. From there it fills in the spacebetween the casing and the actual wellbore, and hardens. This creates aseal so that outside materials cannot enter the well flow, as well aspermanently positions the casing in place.

The method may further include allowing the poly(lactic acid) to degradewhen in contact with water at a temperature of greater than or equal to100° C., greater than or equal to 120° C., greater than or equal to 140°C., or greater than or equal to 160° C. after curing the cement slurry.The temperature may be greater than or equal to 100° C. and less than orequal to 300° C., greater than or equal to 100° C. and less than orequal to 200° C., greater than or equal to 100° C. and less than orequal to 150° C., greater than or equal to 120° C. and less than orequal to 300° C., greater than or equal to 120° C. and less than orequal to 200° C., greater than or equal to 120° C. and less than orequal to 150° C., greater than or equal to 140° C. and less than orequal to 300° C., greater than or equal to 140° C. and less than orequal to 200° C., or greater than or equal to 140° C. and less than orequal to 150° C.

Additionally or alternatively, the method may further include allowingthe poly(lactic acid) to degrade when in contact with water at basicconditions after curing the cement slurry due to the pH of the cement.The cement may have a basic pH of from 8 to 14, from 8 to 12, from 8 to10, from 10 to 14, from 10 to 12, or from 12 to 14. Basic conditions mayinclude a pH of greater than 7, such as a pH of from 8 to 14, from 8 to12, from 8 to 11, from 8 to 10, from 8 to 9, from 9 to 14, from 9 to 12,from 9 to 11, from 9 to 10, from 10 to 14, from 10 to 12, from 10 to 11,from 11 to 14, from 11 to 12, or from 12 to 14. It is contemplated thatthe temperature and pH may be controlled to affect the degradation rateof the poly(lactic acid), such that the poly(lactic acid) may bedegraded at a slower or faster rate depending on the requirements of aspecific application. For instance, the poly(lactic acid) may bedegraded at a relatively faster rate if the cured cement is anticipatedto contact water relatively soon. Alternatively, the poly(lactic acid)may be degraded at a relatively slower rate to avoid reaction prior tothe cement setting or if the cured cement is not anticipated to contactwater relatively soon.

The method may then include allowing the metal oxide to contact waterafter allowing the poly(lactic acid) to degrade after curing the cementslurry, thereby expanding the metal oxide. In embodiments, the metaloxide may expand after contact with water by forming crystal.Specifically, MgO may react with water (H₂O) to form a Mg(OH)₂ crystal.Similarly, in embodiments, CaO may react with water (H₂O) to form aCa(OH)₂ crystal, or both.

As stated previously, the poly(acrylic acid) block copolymer includes at-butyl terminal group, an isobornyl terminal group, or both. Inembodiments, the poly(acrylic acid) block copolymer may comprisepoly(acrylic acid)-block-poly(tert-butyl acrylate). Alternatively oradditionally to the methods previously described, in embodiments, themethod may further include allowing the poly(acrylic acid) blockcopolymer to deprotect when in contact with the acid catalyst at atemperature of greater than or equal to 100° C., greater than or equalto 120° C., greater than or equal to 140° C., or greater than or equalto 160° C. after pumping the cement slurry into the annulus, therebyremoving the t-butyl terminal group, an isobornyl terminal group, orboth, and thereby forming a hydrophilic homopolymer of poly(acrylicacid). The block copolymer structure of the poly(acrylic acid) blockcopolymer may be beneficial because the block of poly(acrylic acid) actsas an anchoring group on the metal oxide while the block ofpoly(tert-butyl acrylate) group acts as a latent initiation site wherethe presence of the acid catalyst under heating can lead to deprotectionof the poly(acrylic acid) block copolymer as previously described. Thetemperature may be greater than or equal to 100° C. and less than orequal to 300° C., greater than or equal to 100° C. and less than orequal to 200° C., greater than or equal to 100° C. and less than orequal to 150° C., greater than or equal to 120° C. and less than orequal to 300° C., greater than or equal to 120° C. and less than orequal to 200° C., greater than or equal to 120° C. and less than orequal to 150° C., greater than or equal to 140° C. and less than orequal to 300° C., greater than or equal to 140° C. and less than orequal to 200° C., or greater than or equal to 140° C. and less than orequal to 150° C.

The method may further include allowing the hydrophilic homopolymer ofpoly(acrylic acid) to degrade when in contact with water at atemperature of greater than 100° C. after curing the cement slurry. Inembodiments, the poly(lactic acid) or poly(acrylic acid) may degradewhen in contact with water in temperatures from 100° C. to 500° C., from100° C. to 200° C., from 100° C. to 180° C., from 100° C. to 175° C.,from 150° C. to 200° C., from 150° C. to 180° C., from 170° C. to 200°C., from 170° C. to 180° C., or from 175° C. to 180° C. In embodiments,degradation may begin to occur at 100° C., 120° C., 150° C., 170° C., or177° C. The method may further include allowing the metal oxide tocontact water after allowing the poly(acrylic acid) to degrade aftercuring the cement slurry, thereby expanding the metal oxide. Inembodiments, the metal oxide may expand after contact with water byforming a Mg(OH)₂ crystal, a Ca(OH)₂ crystal, or both.

Embodiments of the disclosure also relate to methods of producing curedcements. The method may include combining water with a cement precursormaterial and an expanding agent as described herein to form a cementslurry. The cement slurry may be in accordance with any of theembodiments previously described. The method may include curing thecement slurry by allowing for a reaction between the water and thecement precursor material to produce cured cement. The curing step maybe in accordance with any of the embodiments previously described.

In some embodiments, cement is composed of four main components:tricalcium silicate (Ca₃O₅Si), which contributes to the early strengthdevelopment; dicalcium silicate (Ca₂SiO₄), which contributes to thefinal strength, tricalcium aluminate (Ca₃Al₁₂O₆), which contributes tothe early strength; and tetracalcium alumina ferrite. These phases aresometimes called alite and belite respectively. In addition, gypsum maybe added to control the setting time of cement.

Cement slurry design is based on altering the hydration reactions byadding or removing specific additives. In one embodiment, the silicatesphase in cement may be about 75-80 wt. % of the total material. Ca₃O₅Siis the major constituent, with concentration as great as 60-65 wt. %.The quantity of Ca₂SiO₄ conventionally does not exceed 20 wt. %, 30 wt.% or 40 wt. %. The hydration products for Ca₃O₅Si and Ca₂SiO₄ arecalcium silicate hydrate (Ca₂H₂O₅Si) and calcium hydroxide (Ca(OH)₂),also known as Portlandite. The calcium silicate hydrate commonly calledCSH gel has a variable C:S and H:S ratio depending on the temperature,calcium concentration in the aqueous phase, and the curing time. The CSHgel comprises +/−70 wt. % of fully hydrated Portland cement at ambientconditions and is considered the principal binder of hardened cement.Upon contact with water, the gypsum may partially dissolve, releasingcalcium and sulphate ions to react with the aluminate and hydroxyl ionsto form a calcium trisulphoaluminate hydrate (known as the mineralettringite (Ca₆Al₂(SO₄)₃(OH)₁₂.26H₂O)). The ettringite will precipitateonto the Ca₃O₅Si surfaces, thereby preventing further rapid hydration.The gypsum is gradually consumed and the ettringite continues toprecipitate until the gypsum is consumed. The sulphates ionconcentration will decrease and the ettringite will become unstableconverting to calcium monosulphoaluminate hydrate (Ca₄Al₂O₆(SO₄)·14H₂O).The remaining unhydrated Ca₃O₅Si will form calcium aluminate hydrate.

The cured cement may include one or more of calcium hydroxide,silicates, oxides, belite (Ca₂SiO₅), alite (Ca₃SiO₄), tricalciumaluminate (Ca₃Al₁₂O₆), tetracalcium aluminoferrite (Ca₄Al₂Fe₂O₁₀),brownmilleriate (4CaO·Al₂O₃·Fe₂O₃), gypsum (CaSO₄·2H₂O) sodium oxide,potassium oxide, limestone, lime (calcium oxide), hexavalent chromium,trivalent chromium, calcium aluminate, or combinations of these. Thecement precursor material may include Portland cement, siliceous flyash, calcareous fly ash, slag cement, silica fume, or combinations ofany of these.

As described previously, the expanding agent within the cured cement mayexpand after contact with water at temperatures greater than or equal to100° C. and less than or equal to 300° C., greater than or equal to 100°C. and less than or equal to 200° C., greater than or equal to 100° C.and less than or equal to 150° C., greater than or equal to 120° C. andless than or equal to 300° C., greater than or equal to 120° C. and lessthan or equal to 200° C., greater than or equal to 120° C. and less thanor equal to 150° C., greater than or equal to 140° C. and less than orequal to 300° C., greater than or equal to 140° C. and less than orequal to 200° C., or greater than or equal to 140° C. and less than orequal to 150° C. As previously stated, the poly(lactic acid) orpoly(acrylic acid) may degrade at these temperatures, allowing the waterto contact the metal oxide, thereby expanding the metal oxide. The metaloxide may then form a Mg(OH)₂ crystal, a Ca(OH)₂ crystal, or both. Thehydroxide crystal may form within the cured cement, thereby expandingthe volume of the cured cement and providing further sealing againstwater or hydrocarbon seepage from a subsurface formation and preservingthe integrity of the wellbore.

Compressive strength is the resistance of a material to breaking undercompression. A material with a greater compressive strength suffers lessfracturing at a given pressure as compared to a material with a lessercompressive strength. Greater compressive strength is desirable forcured cements in a wellbore, as the cured cement is less likely tofracture in downhole conditions, where pressure may be greater than 20psi, 200 psi, 500 psi, 1000 psi, 2000 psi, 3000 psi, 5000 psi, 7000 psi,or 10000 psi. The cured cement of the present disclosure may have acompressive strength of from 1000 to 7000 psi, from 1000 to 6000 psi,from 1000 to 5500 psi, from 1000 to 5200 psi, from 1000 to 5000 psi,from 1000 to 4700 psi, from 1000 to 4500 psi, from 1000 to 4100 psi,from 1000 to 3500 psi, from 1000 to 3000 psi, from 1000 to 2000 psi,from 2000 to 7000 psi, from 2000 to 6000 psi, from 2000 to 5500 psi,from 2000 to 5200 psi, from 2000 to 5000 psi, from 2000 to 4700 psi,from 2000 to 4500 psi, from 2000 to 4100 psi, from 2000 to 3500 psi,from 2000 to 3000 psi, from 3000 to 7000 psi, from 3000 to 6000 psi,from 3000 to 5500 psi, from 3000 to 5200 psi, from 3000 to 5000 psi,from 3000 to 4700 psi, from 3000 to 4500 psi, from 3000 to 4100 psi,from 3000 to 3500 psi, from 3500 to 7000 psi, from 3500 to 6000 psi,from 3500 to 5500 psi, from 3500 to 5200 psi, from 3500 to 5000 psi,from 3500 to 4700 psi, from 3500 to 4500 psi, from 3500 to 4100 psi,from 4000 to 7000 psi, from 4000 to 6000 psi, from 4000 to 5500 psi,from 4000 to 5200 psi, from 4000 to 5000 psi, from 4000 to 4700 psi,from 4000 to 4500 psi, from 4500 to 7000 psi, from 4500 to 6000 psi,from 4500 to 5500 psi, from 4500 to 5200 psi, from 4500 to 5000 psi,from 4500 to 4700 psi, from 4700 to 7000 psi, from 4700 to 6000 psi,from 4700 to 5500 psi, from 4700 to 5200 psi, from 4700 to 5000 psi,from 5000 to 7000 psi, from 5000 to 6000 psi, from 5000 to 5500 psi,from 5000 to 5200 psi, from 5200 to 7000 psi, from 5200 to 6000 psi,from 5200 to 5500 psi, from 5500 to 7000 psi, from 5500 to 6000 psi,from 6000 to 7000 psi, or from 4000 to 5200 psi, meaning that the curedcement will not fracture until its compressive strength has beenexceeded.

Tensile strength is the resistance of a material to breaking undertension. A material with a greater tensile strength suffers lessfracturing at a given tension as compared to a material with a lessertensile strength. The cured cement of the present disclosure may have atensile strength of from 300 to 600 psi, from 300 to 550 psi, from 300to 525 psi, from 300 to 500 psi, from 300 to 450 psi, from 450 to 500psi, from 450 to 525 psi, from 480 to 520 psi, from 450 to 550 psi, from450 to 600 psi, from 500 to 525 psi, from 500 to 550 psi, from 500 to600 psi, from 525 to 550 psi, from 525 to 600 psi, or from 550 to 600psi, meaning that the cured cement will not fracture until its tensilestrength has been exceeded.

In some embodiments, the cement slurry may contain water and may bewater-based. As such, the cement slurry may by hydrophilic, formingstronger bonds with water-wet surfaces. Well sections drilled withnon-aqueous drilling fluids may have oil-wet surfaces, resulting in poorbonding between the well and the cement slurry, as oil and waternaturally repel. Poor bonding may lead to poor isolation and a buildupof unwanted casing-casing or tubing-casing annular pressure. Withoutbeing bound by theory, it is desirable to make the subsurface formationor casing water wet to enhance and improve the bonding between cementand casing and cement and subsurface formation. If the wettability ofthe subsurface formation or casing is oil wet not water wet then thebonding will be poor and could result in small gap(s) or channel(s)between the cement and casing or the cement and subsurface formationthereby resulting in improper wellbore isolation. This improper wellboreisolation could lead to fluid or gas escaping from the well through thisgas or channel due to de-bonding.

It is noted that one or more of the following claims utilize the term“where” or “in which” as a transitional phrase. For the purposes ofdefining the present technology, it is noted that this term isintroduced in the claims as an open-ended transitional phrase that isused to introduce a recitation of a series of characteristics of thestructure and should be interpreted in like manner as the more commonlyused open-ended preamble term “comprising.” For the purposes of definingthe present technology, the transitional phrase “consisting of” may beintroduced in the claims as a closed preamble term limiting the scope ofthe claims to the recited components or steps and any naturallyoccurring impurities. For the purposes of defining the presenttechnology, the transitional phrase “consisting essentially of” may beintroduced in the claims to limit the scope of one or more claims to therecited elements, components, materials, or method steps as well as anynon-recited elements, components, materials, or method steps that do notmaterially affect the novel characteristics of the claimed subjectmatter. The transitional phrases “consisting of” and “consistingessentially of” may be interpreted to be subsets of the open-endedtransitional phrases, such as “comprising” and “including,” such thatany use of an open ended phrase to introduce a recitation of a series ofelements, components, materials, or steps should be interpreted to alsodisclose recitation of the series of elements, components, materials, orsteps using the closed terms “consisting of” and “consisting essentiallyof.” For example, the recitation of a composition “comprising”components A, B, and C should be interpreted as also disclosing acomposition “consisting of” components A, B, and C as well as acomposition “consisting essentially of” components A, B, and C. Anyquantitative value expressed in the present application may beconsidered to include open-ended embodiments consistent with thetransitional phrases “comprising” or “including” as well as closed orpartially closed embodiments consistent with the transitional phrases“consisting of” and “consisting essentially of.”

As used in the Specification and appended Claims, the singular forms“a”, “an”, and “the” include plural references unless the contextclearly indicates otherwise. The verb “comprises” and its conjugatedforms should be interpreted as referring to elements, components orsteps in a non-exclusive manner. The referenced elements, components orsteps may be present, utilized or combined with other elements,components or steps not expressly referenced.

It should be understood that any two quantitative values assigned to aproperty may constitute a range of that property, and all combinationsof ranges formed from all stated quantitative values of a given propertyare contemplated in this disclosure. The subject matter of the presentdisclosure has been described in detail and by reference to specificembodiments. It should be understood that any detailed description of acomponent or feature of an embodiment does not necessarily imply thatthe component or feature is essential to the particular embodiment or toany other embodiment.

It should be apparent to those skilled in the art that variousmodifications and variations may be made to the embodiments describedwithin without departing from the spirit and scope of the claimedsubject matter. Thus, it is intended that the specification cover themodifications and variations of the various embodiments described withinprovided such modification and variations come within the scope of theappended claims and their equivalents. Unless otherwise stated withinthe application, all tests, properties, and experiments are conducted atroom temperature and atmospheric pressure.

Having described the subject matter of the present disclosure in detailand by reference to specific embodiments of any of these, it is notedthat the various details disclosed within should not be taken to implythat these details relate to elements that are essential components ofthe various embodiments described within, even in cases where aparticular element is illustrated in each of the drawings that accompanythe present description. Further, it should be apparent thatmodifications and variations are possible without departing from thescope of the present disclosure, including, but not limited to,embodiments defined in the appended claims. More specifically, althoughsome aspects of the present disclosure are identified as particularlyadvantageous, it is contemplated that the present disclosure is notnecessarily limited to these aspects.

What is claimed is:
 1. A cement slurry comprising: water; a cementprecursor material; and an expanding agent comprising at least apoly(lactic acid)-metal oxide nanocomposite, where the metal oxidecomprises MgO, CaO, or both, and the poly(lactic acid) comprises acarboxylic acid terminal group.
 2. The cement slurry of claim 1, inwhich the poly(lactic acid) having the carboxylic acid terminal group isa reaction product of poly(lactic) acid and succinic anhydride, maleicanhydride, or both.
 3. The cement slurry of claim 1, in which theexpanding agent has a structure of:

where XO is MgO and x is from 1 to
 100. 4. The cement slurry of claim 1,in which the expanding agent has a structure of:

where XO is CaO and x is from 1 to
 100. 5. The cement slurry of claim 1,in which the cement precursor material comprises one or more componentsselected from the group consisting of calcium hydroxide, silicates,belite (Ca₂SiO₅), alite (Ca₃SiO₄), tricalcium aluminate (Ca₃Al₂O₆),tetracalcium aluminoferrite (Ca₄Al₂Fe₂O₁₀), brownmillerite(4CaO·Al₂O₃·Fe₂O₃), gypsum (CaSO₄·2H₂O), lime (calcium oxide), calciumaluminate, or combinations of these.
 6. The cement slurry of claim 1, inwhich the cement slurry contains from 0.1 to 10 wt. % BWOC of one ormore additives selected from the group consisting of accelerators,retarders, extenders, suspending agents, weighting agents, fluid losscontrol agents, lost circulation control agents, surfactants,antifoaming agents, or combinations of these.
 7. The cement slurry ofclaim 1, in which the cement precursor material comprises Portlandcement precursor, siliceous fly ash, calcareous fly ash, slag cement, orcombinations of these.
 8. A method of cementing a casing in a wellbore,the method comprising: pumping a cement slurry into an annulus betweenthe casing and the wellbore, where the cement slurry comprises: water; acement precursor material; and an expanding agent comprising at least apoly(lactic acid)-metal oxide nanocomposite, where the metal oxidecomprises MgO, CaO, or both, and the poly(lactic acid) comprises acarboxylic acid terminal group; and curing the cement slurry to cementthe casing in the wellbore.
 9. The method of claim 8, further comprisingallowing the poly(lactic acid) to degrade when in contact with water ata temperature of greater than 100° C. after curing the cement slurry.10. The method of claim 9, further comprising allowing the metal oxideto contact water after allowing the poly(lactic acid) to degrade aftercuring the cement slurry, thereby expanding the metal oxide.
 11. Themethod of claim 10, in which the metal oxide expands after contact withwater by forming a Mg(OH)₂ crystal, a Ca(OH)₂ crystal, or both.
 12. Themethod of claim 8, in which the poly(lactic acid) modified with acarboxylic acid terminal group is a reaction product of poly(lactic)acid and succinic anhydride, maleic anhydride, or both.
 13. The methodof claim 8, in which the expanding agent has a structure of:

where XO is MgO and x is from 1 to
 100. 14. The method of claim 8, inwhich the expanding agent has a structure of:

where XO is CaO and x is from 1 to
 100. 15. The method of claim 8, inwhich the cement precursor material comprises one or more componentsselected from the group consisting of calcium hydroxide, silicates,belite (Ca₂SiO₅), alite (Ca₃SiO₄), tricalcium aluminate (Ca₃Al₂O₆),tetracalcium aluminoferrite (Ca₄Al₂Fe₂O₁₀), brownmillerite (4CaO·Al₂O₃Fe₂O₃), gypsum (CaSO₄·2H₂O), lime (calcium oxide), calciumaluminate, or combinations of these.
 16. The method of claim 8, in whichthe cement slurry contains from 0.1 to 10 wt. % BWOC of one or moreadditives selected from the group consisting of accelerators, retarders,extenders, suspending agents, weighting agents, fluid loss controlagents, lost circulation control agents, surfactants, antifoamingagents, or combinations of these.